In a 34‑year‑old woman with a double‑J ureteral stent, bilateral moderate hydronephrosis, recent chemotherapy for cervical cancer, and leukocytosis with neutrophilia, whose urine culture grows Enterococcus faecalis and who has been afebrile for 48 hours on ceftriaxone, should I change therapy to ampicillin (ampicillin) or linezolid (linezolid)?

Switch to Ampicillin Immediately

You must change from ceftriaxone to ampicillin now because enterococci are intrinsically resistant to ceftriaxone and all cephalosporins—the patient's clinical stability despite ceftriaxone indicates either a low bacterial burden or that the infection is not yet adequately treated. 1

Why Ceftriaxone is Ineffective

• Enterococcus faecalis is inherently resistant to all cephalosporins, including ceftriaxone. These agents used alone provide no coverage for enterococcal infections. 1
• The patient's afebrile status for 48 hours does not validate ceftriaxone efficacy—it may reflect the host immune response in a patient with a ureteral stent allowing drainage, not antimicrobial activity against the pathogen. 2
• The persistent leukocytosis (WBC 20,000) with neutrophilia suggests ongoing infection despite apparent clinical improvement. 2

Ampicillin is the Correct Choice

Ampicillin is the drug of choice for ampicillin-susceptible Enterococcus faecalis infections. 2, 3

• For catheter-associated enterococcal infections, ampicillin monotherapy is appropriate for uncomplicated cases when source control is achieved (stent removal or replacement). 2, 3
• The recommended duration is 7-14 days for uncomplicated urinary tract infections with enterococci when the catheter (DJ stent) is removed or replaced. 2, 4
• If the stent must be retained, combination therapy with ampicillin plus gentamicin may be more effective than monotherapy, though this is based on catheter-related bloodstream infection data. 1, 2

Why Not Linezolid

Linezolid is reserved for ampicillin-resistant or vancomycin-resistant Enterococcus faecalis. 1, 2, 3

• Your culture shows 50,000 CFU/mL of E. faecalis—you must obtain antibiotic susceptibility testing immediately to confirm ampicillin susceptibility. 2
• Linezolid would only be appropriate if susceptibilities return showing ampicillin resistance, which is uncommon in E. faecalis (only ~2% of E. faecalis are ampicillin-resistant, compared to 60% of E. faecium). 1
• Using linezolid empirically when ampicillin would likely be effective represents inappropriate antimicrobial stewardship and exposes the patient to unnecessary adverse effects (thrombocytopenia, gastrointestinal effects). 5

Critical Management Steps

Remove or replace the DJ stent if clinically feasible. Source control is critical for enterococcal urinary tract infections and significantly impacts outcomes. 4

• The bilateral hydronephrosis indicates obstructive uropathy—the stent is necessary for drainage, but an infected foreign body perpetuates infection. 4
• Consider stent exchange rather than removal given the bilateral obstruction. 4

Obtain blood cultures immediately given the leukocytosis and recent chemotherapy (immunocompromised state). 4, 3

• Catheter-associated UTI can progress to bacteremia, particularly in immunocompromised patients. 4
• If bacteremia is present, treatment duration extends to 7-14 days for uncomplicated cases or 4-6 weeks if complicated by endocarditis or persistent bacteremia. 2, 3

Monitor for endocarditis if fever recurs or bacteremia persists >4 days, as this is independently associated with mortality. 1, 2

• Consider transesophageal echocardiography if signs/symptoms suggest endocarditis or if bacteremia persists despite appropriate therapy. 2

Practical Antibiotic Regimen

Start ampicillin 2 grams IV every 6 hours (or 12 grams/day by continuous infusion). 6

• Once susceptibilities confirm ampicillin susceptibility and clinical improvement is documented, consider transition to oral amoxicillin 500 mg every 8 hours to complete therapy. 3
• Obtain follow-up urine cultures 48-72 hours after initiating ampicillin to document response. 4

If ampicillin resistance is documented, switch to vancomycin (if vancomycin-susceptible) or linezolid/daptomycin (if vancomycin-resistant). 1, 2

Common Pitfall to Avoid

Do not continue ceftriaxone based on clinical improvement—this creates a false sense of adequate treatment while allowing potential progression to complicated infection (pyelonephritis, bacteremia, sepsis) in an immunocompromised patient with obstructive uropathy. 1, 4